Numerous cases have been reported where zircon may have precipitated from a hydrothermal fluid or a fluid-saturated residual melt. Temperatures for hydrothermal zircon formation range from 600°C in late-magmatic systems at the magmatic-to-hydrothermal transition down to 300°C in mesothermal ore-forming systems. Late-magmatic to hydrothermal zircon may precipitate from fluid-saturated magma and possibly from the fluids exsolved from mineralized granites and pegmatites. For example, in the Sn-W-mineralized Mole Granite, New South Wales, Australia, zircon occurs in growth zones in hydrothermal quartz, along with monazite, xenotime and thorite (Fig. 1). This zircon - considered to be hydrothermal - preserves a...